HONG KONG (Reuters) - Thousands of people rallied in Hong Kong on Sunday to demand justice for a young Indonesian maid who was badly beaten by her employer in a case that has sparked widespread outrage and a police investigation into accusations of torture.

The ill-treatment of foreign domestic workers in Asian and Gulf regions such as Hong Kong, Singapore, Taiwan and Dubai has been a longstanding problem but the severe injuries suffered by the Indonesian maid have drawn fresh attention to the risks faced by this migrant community.

"We are workers. We are not slaves," chanted a crowd of several thousand domestic workers and their supporters as they marched to Hong Kong's government headquarters.

Some waved the red and white flag of Indonesia, while others held up grisly photographs of the battered face and body of the 23-year-old maid, Erwiana Sulistyaningsih.

"We have to end modern day slavery like this," said Ila Hasan, 32, a domestic worker from Indonesia's island of Java, who wore a red shawl and a blue bandana emblazoned with the word 'Justice'.

"The employer isn't human. These things shouldn't happen."

Hong Kong, a former British territory that returned to Chinese rule in 1997, has around 300,000 foreign domestic helpers, most of them from the Philippines and Indonesia.

While cases of such harsh treatment are rare, Hong Kong's policies on migrant workers have often made maids reluctant to report abuse for fear of losing their livelihoods and being deported if they fail to find new jobs swiftly.

Hong Kong police and the labour bureau are now investigating the case and will interview Erwiana on Monday, said Eni Lestari, the head of advocacy group the International Migrants' Alliance, which has been in close touch with the victim.

A second maid, identified only as Susi, who claimed to have been abused by the same employer, also gave statement to police, saying she had frequently been beaten and abused.

No formal charges have yet been made against the Hong Kong employer, who also reportedly threatened to kill Erwiana and her family if she revealed the abuse she suffered.

Erwiana is now recovering from her injuries at a
hospital in Sragen, a city in central Java, after flying out from Hong Kong in early January.

"I want the ones who tortured and wronged my daughter to be prosecuted and have justice done," said her father, Rohmad Saputra, speaking at her bedside.

The maid had suffered extensive injuries but her condition was stabilising, a hospital spokesman said.

"She was subjected to intense heat. Most of the bruises are on the face, legs and arms. And she is in a very poor, weak condition," said Sri Yoko, the spokesman.

"Even what should be light activity is difficult for her. Now the progress is very good, but she still hasn't been communicating properly."

Rights groups demanded a review of Hong Kong's migrant worker policies to tackle issues such as overcharging by job agencies and the "two-week rule", referring to the deadline by which maids must leave the city after losing their jobs.

"This is not an isolated case," said Lestari, who estimates her group receives four to six complaints of physical assault each month from
maids in Hong Kong.

"The only difference is we were able to bring it to the public and to the media and that put pressure on the police."